The present invention relates to the art of diagnostic imaging. It finds particular application in conjunction with nuclear or gamma cameras and single photon emission computed tomography (SPECT) and will be described with particular reference thereto. It is to be appreciated, however, that the present invention will also find application in other non-invasive investigation techniques and imaging systems such as single photon planar imaging, whole body nuclear scans, positron emission tomography (PET) and other diagnostic modes.
In diagnostic nuclear imaging, one or more radiation detectors are mounted on a movable gantry to view an examination region which receives a subject therein. Typically, one or more radiopharmaceuticals or radioisotopes such as 99mTc or 18F-Fluorodeoxyglucose (FDG) capable of generating emission radiation are introduced into the subject. The radioisotope preferably travels to an organ of interest whose image is to be produced. The detectors scan the subject along a selected path or scanning trajectory and radiation events are detected on each detector.
In a traditional scintillation detector, the detector includes a scintillation crystal that is viewed by an array of photomultiplier tubes. A collimator which includes a grid- or honeycomb-like array of radiation absorbent material is located between the scintillation crystal and limits the angle of acceptance of radiation which will be received by the scintillation crystal. The relative outputs of the photomultiplier tubes are processed and corrected to generate an output signal indicative of the position and energy of the detected radiation. The radiation data is then reconstructed into an image representation of a region of interest.
A so-called rotating laminar radionuclide camera (xe2x80x9cROLECxe2x80x9d) has been disclosed by Tosswill and others. Devices utilizing a cadmium telluride (CdTe) detector arrangement have been disclosed in Mauderli, et al., A Computerized Rotating Laminar Radionuclide Camera, J. Nucl. Med 20: 341-344 (1979) and Entine, et al., Cadmium Telluride Gamma Camera, IEEE Transactions on Nuclear Science, Vol. NS-26, No. 1: 552-558 (1979). According to one version, the device included a linear array of CdTe detectors separated by tungsten plates that confined the field of view of each detector to one dimension. The device had a square (approximately 4 cmxc3x974 cm) active area, although a circular lead mask reduced the active area to 13.2 cm2. The detectors, which had platinum-film electrodes, were attached to copper strips on a printed circuit board that also served as the base of the collimator and as a support for amplifier-discriminator circuits.
A ROLEC having a 250 mmxc3x97250 mm active area was disclosed in Tosswill, U.S. Pat. No. 4,090,080, issued May 16, 1978 and entitled Imaging. The device included scintillating plastic sheets disposed between parallel collimator plates supported by a steel frame. Fiber optics epoxied to the rear surface of each scintillating sheet transferred light generated in the each of the detectors to a corresponding photomultiplier. According to Tosswill, the ROLEC may be operated moving its axis along another curved or other configuration or without rotation, with symmetry preferred but not essential.
Devices using a segmented germanium crystal have been described by Urie, et al., Rotating Laminar Emission Camera with GE-detector, Med. Phys. 8(6): 865-870 (1981); Mauderli, et al., Rotating Laminar Emission Camera with GE-Detector: An Analysis, Med. Phys. 8(6): 871-876 (1981); Malm, et al., A Germanium Laminar Emission Camera, IEEE Transactions on Nuclear Science, Vol. NS-29, No. 1: 465-468 (1982); and Mauderli, et al., Rotating Laminar Emission Camera with GE-detector: Further Developments, Med. Phys. 14(6): 1027-1031 (1987).
In a first version, a 11.5 mm thick, 45 mmxc3x9745 mm segmented germanium detector was placed behind parallel tungsten plates. The crystal was segmented to form a plurality of channels, with the plates aligned with the segmentations. A 4.5 cm diameter viewing aperture was located between the detector and the activity source. Projection data acquired at multiple angular orientations as the detector-collimator assembly was rotated about its center was mathematically reconstructed to form a two-dimensional image of the activity distribution.
A second version simulated a 195 mmxc3x97195 mm detection area. Five germanium blocks having a total length of 250 mm segmented into distinct electrical channels. The detector was translated linearly in a direction perpendicular to the plane of the plates to simulate a full-size detector.
One advantage of ROLECs is their high efficiency relative to traditional Anger cameras. In particular, the structure of the collimator permits a greater percentage of incident radiation to reach the surface of the detector. Spatial resolution may be improved by increasing the height of the collimator or reducing the distance between the collimator elements with less effect on efficiency as compared to traditional cameras.
While ROLECs have the advantage of relatively higher efficiency and spatial resolution, they have been expensive to produce inasmuch as significant quantities of relatively expensive detector material have been required. Although detector material cost can be reduced by using a number of relatively smaller detector segments, such an approach complicates the manufacturing process and requires that variations in the response of the individual segments be considered.
Still another drawback is that the collimator slat length has been equal to the detector field of view. This has required additional detector, collimator, and structural material, has introduced spurious counts which do not contribute to useful image information, and has introduced additional mass and bulk into a rotating structure.
Yet another disadvantage to ROLECs has been their circular field of view.
Embodiments of the present invention address these matters, and others.
According to a first aspect of the present invention, a rotating laminar radionuclide camera has a non-circular field of view. According to a more limited aspect, the field of view is substantially squre. According to another more limited aspect the detector ratio of the camera is greater than one. According to a still more limited aspect, the camera includes a cadmium zinc telluride radiation sensitive detector.
According to another aspect of the present invention, a radiation detection apparatus includes a gamma radiation detector having a plurality of spaced apart radiation attenuative septa. The apparatus also includes a drive operatively connected to the detector so as to cause a rotation of the detector about an axis of rotation and a translation of the axis of rotation such that the detector has a non-circular field of view.
According to a more limited aspect of the present invention, the ends of the detector trace a substantially square path.
According to another more limited aspect, the field of view is substantially square. According to a still more limited aspect, the motion of the detector is such that a plurality of points on the detector follow a circular path in relation to the centroid of a curve of constant width rotating within the square. According to a yet more limited aspect, the curve of constant width is a Reuleaux triangle.
According to another more limited aspect of the invention, the detector includes a longitudinal axis. The motion of the detector is such that a point on a line perpendicular to the longitudinal axis and extending between the longitudinal midpoint of the detector and the centroid of Reuleaux triangle rotating within the square follows a path having a curved diamond shape. According to yet another more limited aspect, the motion of the detector is such that a line segment perpendicular to the longitudinal axis and intersecting the longitudinal midpoint of the detector traces the path traveled by the centroid of a curve of constant width rotating within the square.
According to another more limited aspect of the present invention, the detector includes a plurality of detector segments. The transverse dimensions of the detector segments are less than the number of detector segments multiplied by their longitudinal pitch. According to yet another limited aspect of the present invention, the detector has a detector ratio greater than one. According to another limited aspect, the translation and rotation occur simultaneously. According to still another limited aspect, the detector includes a first drive for causing rotation of the detector and a second drive for causing translation of the detector.
According to another aspect of the present invention, a radiation detection method includes using a radiation sensitive detector having a plurality of spaced apart radiation attenuative septa to detect radiation indicative of radionuclide decays, rotating the detector in a plane, and in coordination of with the rotation of the detector, translating the detector so that the detector has a non-circular field of view.
According to a more limited aspect of the invention, the ends of the detector trace a substantially square path. According to a more limited aspect, the motion of the detector is such that a plurality of points on the detector follow a circular path in relation to the centroid of a curve of constant width rotating within a square. According to another more limited aspect, the motion of the detector is such that a point on a line perpendicular to the detector""s longitudinal axis and extending between the longitudinal midpoint of the detector and the centroid of a curve of constant width rotating within a square follows a path having a curved diamond shape. According to another more limited aspect, the motion of the detector is such that a line segment perpendicular to the longitudinal axis and intersecting the longitudinal midpoint of the detector traces the path traveled by the centroid of a Reuleaux triangle rotating within a square.
According to another more limited aspect of the present invention, the detector has a detector ratio greater than one. According to another more limited aspect, the method includes translating the detector during rotation of the detector. According to another more limited aspect of the invention, the method also includes rotating the detector in an orbit about an examination region so as to detect radiation at a plurality of angular positions with respect to the examination region and generating a tomographic image indicative of the detected radiation.
According to another aspect of the present invention, a radiation detection method includes using a detector having a slit collimator to detect gamma radiation indicative of radionuclide decays, rotating the detector about an axis of rotation so as to vary the angular relationship between the slit collimator and an object under examination, and translating the axis of rotation along a closed, non-linear path whereby the detector has a non-circular field of view. According to a still more limited aspect, the path has a curved diamond shape.